Fundus camera

ABSTRACT

An ophthalmologic apparatus including an index projection unit to project an index on a cornea of a subject&#39;s eye, an imaging unit to form an image on an imaging plane via an objective lens and capture an image of the index projected on the cornea, and a control unit to control a distance between the subject&#39;s eye and the object lens so that a size of the captured index becomes a predetermined size.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.12/849,618 filed Aug. 3, 2010, which claims priority to Japanese PatentApplication No. 2009-183339 filed Aug. 6, 2009, both of which are herebyincorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a fundus camera which performsalignment while observing an operation distance index.

2. Description of the Related Art

In a conventional fundus camera, when an operator photographs a fundusimage, a light flux is projected from the periphery of a pupil of asubject's eye, and a fundus reflection light flux is taken out from acenter of the pupil as a photographing light, so that a photographinglight flux has a small diameter. Thus, if the light flux deviates even alittle, the pupil shades the light flux, so that a flare easily entersin an imaging plane. For performing correct positioning, it is necessaryto stabilize a fixation, match alight axis of the subject's eye and anoptical axis of a fundus camera optical system, and adjust alignment toa proper position.

Japanese Patent Application Laid-Open No. 62-34530 discusses a funduscamera which projects an alignment index on a cornea of a subject's eye,and determines whether the alignment index is on a proper alignmentposition in a state that an alignment image which is a reflection imageof the projected alignment index in focus. Japanese Patent ApplicationLaid-Open No. 7-31590 discusses a fundus camera which projects analignment index on a cornea of a subject's eye, and determines whetherthe alignment index is on a proper alignment position based onseparation or matching of an alignment image.

Japanese Patent Application Laid-Open No. 7-31590 and Japanese PatentApplication Laid-Open No. 2000-287934 discuss a technique for moving alight guide for projecting an operation distance index. In thistechnique, the light guide is moved so that a proper operation distancewhen a fundus peripheral part is photographed is becomes longer than theproper operation distance when a fundus center part is photographed.However, this operation is not for detecting the operation distance.

In the above described conventional fundus cameras, since a lightemitting diode (LED) light source having one kind of single wavelengthis used as a light source for an alignment index, it can be determinedwhether the alignment index is in a proper alignment position or not.However, it cannot be determined whether the fundus camera is in a nearposition with respect to a subject's eye or in a far position in theproper alignment position.

Therefore, for operating the fundus camera to a proper alignmentposition, an operator moves the fundus camera once toward eitherdirection of closing to or separating from the subject's eye, anddetermines a direction for closing to the proper alignment positionbased on whether a defocusing degree and a separation degree increase ornot. There is no problem when an operator can move the fundus camera toaright direction for alignment by chance. However, when the operatormoves the fundus camera toward an inverse direction, the operation formoving the camera is wasteful.

SUMMARY OF THE INVENTION

The present invention relates to a fundus camera which can performalignment easily.

According to an aspect of the present invention, a fundus cameraincludes an illumination optical system configured to project aring-shaped illumination light on a pupil of a subject's eye, an imagingoptical system configured to form a fundus image of the illuminationlight from a fundus on an imaging plane via an objective lens, an indexprojection unit configured to project an operation distance index on acornea of the subject's eye via the objective lens, an imaging unitconfigured to capture a reflection image from the fundus and areflection image of the operation distance index from the cornea, adriving unit configured to move the operation distance index in anoptical axis direction of the imaging optical system, an index shaperecognition unit configured to recognize an index shape projected on thecornea according to a movement of a light emitting surface of the indexprojection unit by the driving unit, and a detection unit configured todetect operation distances of the illumination optical system and theimaging optical system with respect to the subject's eye based ondriving information about the driving unit and an output of the indexshape recognition unit.

Other features and advantages of the present invention will be apparentfrom the following description taken in conjunction with theaccompanying drawings, in which like reference characters designate thesame or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features,and aspects of the invention and, together with the description, serveto explain the principles of the invention.

FIG. 1 illustrates an optical configuration of a fundus camera.

FIGS. 2A and 2B are a front view and a side view of a split projectionunit.

FIGS. 3A and 3B are a side view and a front view of an operationdistance index projection unit.

FIG. 4 illustrates a block circuit configuration according to a firstexemplary embodiment.

FIG. 5 illustrates an image projected on a monitor.

FIG. 6 illustrates an optical path of an operation distance detectionoptical system.

FIGS. 7A to 7C illustrate a relationship between positions of a lightemitting surface and an imaging plane, and a size of a bright spotimage.

FIG. 8 is a graph illustrating a relationship between an operationdistance and a size of a bright spot image.

FIG. 9 is a control flowchart for detecting a bright spot.

FIG. 10 is a perspective view illustrating a fundus camera including analignment driving mechanism.

FIG. 11 illustrates a block circuit configuration of a second exemplaryembodiment.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings.

FIG. 1 illustrates an optical configuration of a fundus camera accordingto a first exemplary embodiment.

The fundus camera includes an illumination optical system from a halogenlamp 1 which is a light source for observation to an objective lens 2 infront of a subject's eye. A visible cut filter 3 which can be insertedinto and removed from an optical path, a flash tube 4 which is a lightsource for photographing, a lens 5, and a folding mirror 6 are alignedin front of the halogen lamp 1. In a reflection direction of the foldingmirror 6, a first relay lens 7, a split projection unit 8 for focusing,a second relay lens 9, and a perforated mirror 10 are aligned in thisorder. A hemispherical reflection mirror 11 is provided behind thehalogen lamp 1.

A photographic diaphragm 12 is provided at a hole portion of theperforated mirror 10. In a imaging optical system behind thephotographic diaphragm 12, an operation distance index projection unit13 for detecting an operation distance with respect to a subject's eyeE, a focus lens 14 for focusing on a fundus surface, an imaging lens 15,a quick return mirror 16 for reflecting a part of a visible light, andan imaging unit 17 are aligned. Further, in a reflection direction ofthe quick return mirror 16, a LED is provided in a matrix state, and aninternal fixation target 18 guiding a line-of-sight direction of thesubject's eye is arranged.

FIGS. 2A and 2B illustrate a plane view and a side view of the splitprojection unit 8. The split projection unit 8 includes a split indexlight source 21, an infrared light transmitting body 22, and a splitprism 23 formed on the infrared light transmitting body 22. The splitprojection unit 8 can be inserted into and removed from an illuminationoptical path by a split driving motor 24. The split index light source21 includes an LED light source which emits near infrared light having awavelength of 700 nm, and projects the infrared light to the split prism23 from a direction approximately vertical to the illumination opticalpath.

The split prism 23 is formed at a center part of the optical path, andsplit light is projected to the illumination optical path through thesplit prism 23. When the split light focuses on a fundus Er, two baselines of the split light become a straight line. When the split lightdoes not focus on the fundus Er, the base line is divided into two. Thesplit projection unit 8 is inserted into the illumination optical pathat the time of observation, and retreats immediately from theillumination path at the time of photographing.

FIGS. 3A and 3B are a side view and a front view of the operationdistance index projection unit 13 which is an index projection unit.Outgoing ends 31 a of two light guides 31 are arranged on both sides ofthe photographic diaphragm 12 in the hole portion of the perforatedmirror 10. Distance index light sources 32 including a near infraredlight LED are provided at each incident end 31 b of the light guides 31.The operation distance index projection unit 13 can be moved back andforth with a minute movement by a predetermined amount in the opticalaxis direction of the imaging optical system by a driving unit of adistance index driving motor 33.

An infrared light entered from the incident end 31 b of the light guide31 travels in a straight line, is reflected and changed an angle on thereflection surface, travels straight, and exits from a light emittingsurface P of the outgoing end 31 a. The light emitting surface P is in aconjugate relationship with the objective lens 2 to generate a virtualimage P′ between a cornea Ec of the subject's eye E and a crystallinelens.

FIG. 4 illustrates a block circuit configuration of an electric circuitunit. An output of the imaging unit 17 is connected to a calculationprocessing circuit 42 and a monitor 43 via an image signal processingcircuit 41. Outputs of the calculation processing circuit 42 areconnected to the distance index light source 32 and the distance indexdriving motor 33 of the operation distance index projection unit 13, anda Z-axis driving motor 44 for driving the fundus camera in the opticalaxis direction of the imaging optical system.

At the time of alignment with respect to the subject's eye E, a lightflux emitted from the halogen lamp 1 is made to be infrared light by thevisible cut filter 3, travels through the flash tube 4 and the lens 5,and reaches the folding mirror 6. The infrared light reflected by thefolding mirror 6 travels through the first relay lens 7, the splitprojection unit 8, and the second relay lens 9, and enters into theperforated mirror 10. The light flux reflected by the perforated mirror10 forms a ring light on a pupil of the subject's eye E through theobjective lens 2, and illuminates the fundus Er of the subject's eye E,as infrared light. The reflection light reflected on the fundus Erpasses a center of the ring light on the pupil, and passes an inside ofthe perforated mirror 10 through the objective lens 2. Then, thereflection light forms an image on the photographic diaphragm 12, thefocus lens 14, the imaging lens 15, and the imaging unit 17, and isdisplayed on the monitor 43 illustrated in FIG. 5 as a fundus image Ef.

In the split projection unit 8, an infrared light emitted from the splitindex light source 21 is refracted in a direction of the illuminationoptical path by the split prism 23 arranged on the illumination opticalpath, travels through the perforated mirror 10 and the objective lens 2,and is projected on the fundus Er. A split image S projected on thefundus Er is captured by the imaging unit 17 via the imaging opticalsystem. On the monitor 43, a base line is displayed at a center of thefundus image Ef, and is divided into two according to a movement of thefocus lens 14. When the base line becomes one, the fundus image Ef comesinto focus. An operator can determine frontward defocusing or backwarddefocusing based on a dividing direction of the two base lines.

In the operation distance index projection unit 13, the operationdistance index is projected on the subject's eye E from two lightemitting surfaces P, and a cornea reflection image with two bright spotimages A is formed on the surface of the cornea Ec. The bright spotimages A are formed on the imaging unit 17 and displayed on the monitor43. In a proper alignment state, the bright spot images A are projectedon positions separated from each other by a predetermined distance in acenter horizontal direction of the fundus image Ef.

FIG. 6 illustrates an optical path of an operation distance detectionoptical system. The infrared light emitted from the light emittingsurface P of each light guide 31 travels through the objective lens 2,is refracted at the cornea Ec of the subject's eye E and forms thevirtual image P′. The virtual image P′ is in a conjugate positionalrelationship with a primary image forming surface Lo through theobjective lens 2. The fundus Er is also in a conjugate positionalrelationship with the primary image forming surface Lo with respect tothe objective lens 2. Further, the primary image forming surface Lo isin a conjugation relationship with the imaging unit 17 with respect tothe focus lens 14 and the imaging lens 15.

In such an optical configuration, alight flux emitted from the lightemitting surface P of the light guide 31 is reflected on the cornea Ec,and becomes the bright spot image A. Then, the bright spot image Apasses through the photographic diaphragm 12 in the perforated mirror10, and forms an image on the imaging unit 17 via the focus lens 14 andthe imaging lens 15. A light flux from the illumination optical systembecomes a reflection image on the fundus Er, passes through thephotographic diaphragm 12, and is projected on an imaging plane Lc ofthe imaging unit 17 via the focus lens 14 and the imaging lens 15.Therefore, an image formed on the imaging plane Lc is an image combinedwith the split image S and two bright spot images A of the operationdistance index in the fundus image Ef.

The calculation processing circuit 42 outputs an amount of movementhaving a predetermined cycle as a driving command to the distance indexdriving motor 33 via the motor driver. The distance index driving motor33 moves the light emitting surface P of the light guide 31 minutelyback and forth in the optical axis direction. The bright spot images Aformed on the imaging unit 17 are extracted by the image signalprocessing circuit 41. The distance index light source 32 of theoperation distance index projection unit 13 is blinked under control ofthe calculation processing circuit 42. The image signal processingcircuit 41 calculates a difference between images at a time of turningon and at a time of turning off of the distance index light source 32,and extracts the bright spot image A. Then, the image signal processingcircuit 41 calculates an index shape, i.e., a size, of the bright spotimage A, and recognizes the index shape. The light emitting surface P isautomatically moved minutely back and forth by the predetermined amountin the optical axis direction.

FIGS. 7A to 7C illustrates a relationship between positions of the lightemitting surface P and the imaging plane Lc, and the size of the brightspot image A. FIG. 7A illustrates a relationship of the shape, i.e. thesize of the bright spot image A with respect to a positional deviationΔt of the light emitting surface P by the minute back and forthmovement, when a positional relationship between an optical unit with abuilt-in optical system of the fundus camera and the subject's eye E isa proper distance (WD=D0).

When the light emitting surface P moves in the optical axis direction,the size and blur of the bright spot image A projected on the imagingplane Lc change. In a state of a proper operation distance D0, when thepositional deviation Δt occurs, the size of the bright spot image Abecomes large and blurred (d0<do′=do″).

FIG. 7B illustrates the relationship of the size of the bright spotimage A with respect to the positional deviation Δt of the lightemitting surface P when the positional relationship between the opticalunit and the subject's eye E closes more than the proper distance, i.e.,when the operation distance is short which is WD=D1<D0.

In this case, when the light emitting surface P moves to the subject'seye E side in the optical axis direction, the bright spot image A isformed on a position further away from the imaging plane Lc, so that thebright spot image A becomes further largely blurred. Or when the lightemitting surface P moves to the imaging plane Lc side in the opticalaxis direction, the bright spot image A is projected further small andvividly because the light emitting surface P closes to the imaging planeLc (d1′<d1<d1″).

FIG. 7C illustrates the relationship of the size of the bright spotimage A with respect to the positional deviation Δt of the lightemitting surface P when the positional relationship between the opticalunit and the subject's eye E is separated more than the proper distance,i.e., when the operation distance is long which is WD=D2>D0.

In this case, when the light emitting surface P moves to the subject'seye E side in the optical axis direction, the bright spot image A isformed on a position closer to the imaging plane Lc, so that the brightspot image A is projected further small and vividly. Further, when thelight emitting surface P moves to the imaging plane Lc side in theoptical axis direction, the bright spot image A becomes further largelyblurred because the light emitting surface P separates from the imagingplane Lc (d2″<d2<d2′).

Accordingly, while the positional relationship between the optical unitof the fundus camera and the subject's eye E changes, the light emittingsurface P of the light guide 31 is moved minutely back and forth by thedistance index driving motor 33. Accordingly, it can be determinedwhether the optical unit comes closer to or is separated from the properoperation distance D0 by detecting the relationship of the size of thebright spot image A in a moving direction or the like of the distanceindex driving motor 33.

A detected result is displayed on the monitor 43, and an operator canrecognize a direction to move and adjust the position of the opticalunit back and forth. However, operability can be better that the opticalunit is automatically positioned at the proper operation distance basedon the detected result of the bright spot image A. In the block circuitconfiguration in FIG. 4, the fundus camera is driven in the operationdistance direction via the Z-axis driving motor 44, based on thedirection detected by the calculation processing circuit 42 and a methodfor detecting a movement amount described below.

FIG. 8 is a graph illustrating a relationship between a size d of thebright spot image A in a vertical axis and a deviation Dt with respectto the proper operation distance WD=D0 of the optical unit in ahorizontal axis. In the operation distance D2 where the operationdistance WD is larger than the proper distance W0, when the lightemitting surface P is minutely moved in a reciprocation period, the sizeof the bright spot image A changes as described above, so that therelationship becomes d2″<d2<d2′.

In the relationship of d2′−d2″>0, control is performed to move theoptical unit closer to the proper operation distance D0 by a specificamount in proportion to a ratio of d2′/d2″. When the operation distanceWD has a value D3 which is larger than a value D2, the control to movethe optical unit closer to the proper operation distance D0 can beperformed similarly.

When the operation distance WD has a value D1 which is smaller than avalue of the proper distance D0, the relationship becomes d1′−d1″<0, sothat the control is performed to move the optical unit closer to theproper operation distance D0 by a specific amount in proportion to aratio of d1″/d1′ in an inverse direction. By this operation, the opticalunit can be driven in the proper operation distance D0. Therefore, theoperation distance WD can be detected by the movement of the lightemitting surface A and the recognition and determination of the brightspot image A.

FIG. 9 is a flowchart illustrating processing for associating therecognition of the bright spot image A which is a projection index anddriving information about the operation distance. The image signalprocessing circuit 41 extracts the bright spot image A received by theimaging unit 17. In step S1, when the bright spot image A is extracted,the driving unit minutely moves the light emitting surface P back andforth of a predetermined amount. In step S2, the image signal processingcircuit 41 extracts the bright spot images at a center and maximumpositions in back and forth directions of the reciprocation movement ofthe light emitting surface P. In steps S3 to S5, a state of the opticalunit is determined according to the size of the bright spot image Abasedon FIGS. 7A to 7C and FIG. 8.

More specifically, when dn″<dn<dn′ is satisfied (YES in step S3), thenin step S6, the optical unit is moved backward so as to separate fromthe subject's eye E, and processing proceeds to step S5. When dn″<dn<dn′is satisfied (YES in step S4), then in step S7, the fundus camera ismoved forward so as to come closer to the subject's eye E, andprocessing proceeds to step S5. In step S5, when dn<dn′=dn″ is satisfied(YES in step S5), it is determined that the fundus camera is at theproper operation distance D0, and the fundus camera enters into ashooting standby state. In step S8, the operator pushes a shootingswitch to perform shooting (YES in step S8), and processing ends. Instep 5, when dn<dn′=dn″ is not satisfied (NO in step S5), the processingreturns to step S1, and the processing in the flow is repeated again.

When a fundus is photographed, the split projection unit 8 retreats fromthe optical path. When the alignment and the focus between the opticalunit and the subject's eye E are properly adjusted, the operator canpush the shooting switch to perform shooting. At the time of shooting, alight flux of white light emitted from the flash tube 4 travels throughthe folding mirror 6 and the first and second relay lenses 7 and 9, isreflected on the perforated mirror 10, and forms ring-shaped flashlight. The reflected ring-shaped flash light illuminates the fundus Erthrough the pupil of the subject's eye E. The reflection light from thefundus Er passes the photographic diaphragm 12 of the perforated mirror10, travels through the focus lens 14 and the imaging lens 15, andreaches the imaging unit 17 behind the quick return mirror 16 which ispulled upward out of the optical path, so that the fundus image Ef canbe photographed.

If the alignment driving unit can drive at least only in the operationdistance direction, the fundus camera can be automatically positioned tothe proper operation distance by detecting the proper operation distanceand feeding back the detected result to an alignment driving system asdescribed above.

When the positional relationship between the subject's eye E and theoptical unit deviates vertically or horizontally, it can be recognizedthat the bright spot image A deviates vertically or horizontally on theimaging plane of the imaging unit 17. By performing such detection, thepositional deviations can be recognized in a three-dimensional directionin addition to the operation distance direction, and an automaticalignment can be implemented by performing feedback control to positionthe alignment driving unit at the proper position according to theamount of deviation.

FIG. 10 illustrates a perspective view of a fundus camera including theabove described alignment driving mechanism according to a secondexemplary embodiment. The fundus camera includes a main body unit 51 anda face fixation unit 52 for a subject. The main body unit 51 includes anoptical unit 53 with a built-in optical system, and three optical unitdriving units which move the optical unit 53 in X, Y, and Z axialdirections in the three-dimensional space. A groove is formed in the Xaxial direction on a fixation unit 54 which is a base, and a movableunit 55 is inserted into the groove. A female screw portion which isdrilled in the movable unit 55 engages with a male threaded rod 57 of adriving motor 56 fixed at the fixation unit 54.

Similarly, a groove is formed in the Z axial direction on the movableunit 55, and a movable unit 58 is inserted into the groove. The movableunit 58 engages with a driving motor 59 fixed on the movable unit 55 viaa threaded rod 60. Further, a groove is formed in the Y axial directionon the movable unit 58, and the optical unit 53 is inserted into thegroove. The optical unit 53 engages with a driving motor 61 on themovable unit 58 via a threaded rod (not illustrated).

These driving motors 56, 59, and 61 are electrically connected to abelow described calculation control circuit, so that the driving motors56, 59, and 61 can control the optical unit 53 to move to predeterminedpositions in the three-dimensional direction. The driving motors 56, 59,and 61 can be selected from pulse motors and DC motors, for example.However, when a DC motor which cannot quantitatively control rotation isused, it is desirable that an apparatus internally includes a detectionelement which can detect a position by detecting a movement distance ofthe optical unit driving unit and a rotation amount of the drivingmotor.

FIG. 11 illustrates a block circuit configuration for performing motorcontrol for automatic alignment. Outputs of a calculation controlcircuit 71 are connected to the driving motors 56, 59, and 61, a drivingmotor 72 for driving the focus lens 14, the split driving motor 24, thedistance index driving motor 33, and a quick return mirror driving motor73 via respective driver circuits. Further, the output of thecalculation control circuit 71 is connected to the halogen lamp 1, theflash tube 4, the distance index light source 32, and the internalfixation target 18. Furthermore, outputs of the imaging unit 17 and ashooting start switch 74 are connected to the calculation controlcircuit 71.

At the time of automatic alignment, a video signal of the bright spotimage A acquired by the imaging unit 17 which is arranged in the opticalunit 53 is input to the calculation control circuit 71. In addition tothe detection of the operation distance as described above, thecalculation control circuit 71 calculates a deviation amount of thebright spot image A in the vertical and horizontal directions from thepredetermined position on the imaging plane, and transmits a signal tothe driving motors 56, 59, and 61 provided at the optical unit drivingunit so that the bright spot image A is on a predetermined position. Thedriving motor 56, 59, and 61 electrically move the optical unit 53 inthe vertical and horizontal directions based on the signal received fromthe calculation control circuit 71, and perform alignment to a properposition with respect to the subject's eye E.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures, and functions.

This application claims priority from Japanese Patent Application No.2009-183339 filed Aug. 6, 2009, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. An ophthalmologic apparatus comprising; an indexprojection unit configured to project an index on a cornea of asubject's eye; an imaging unit configured to form an image on an imagingplane via an objective lens and capture an image of the index projectedon the cornea; a driving unit configured to move a light-emittingsurface of the index projection unit so as to change a size of theindex; and a control unit configured to control a distance between thesubject's eye and the object lens based on a size of the captured index.2. The ophthalmologic apparatus according to claim 1, wherein a movementof the light emitting surface by the driving unit is a reciprocationmovement.
 3. The ophthalmologic apparatus according to claim 2, whereinthe control unit controls the distance based on a relation between thesize of the captured index and the distance from the light-emittingsurface of the index projection unit to the subject's eye.
 4. Theophthalmologic apparatus according to claim 1, further comprising: anillumination optical system configured to project a ring-shapedillumination light on a pupil of the subject eye; and an imaging opticalsystem configured to form an image of a light flux of the illuminationlight reflected from a fundus on the imaging plane via an object lensand capture a fundus image.
 5. The ophthalmologic apparatus according toclaim 4, wherein the illumination optical system comprises a perforatedmirror configured to reflect illumination light, and wherein the indexprojection unit is disposed in a hole portion of the perforated mirror.6. The ophthalmologic apparatus according to claim 1, wherein thecontrol unit obtains a working distance for the subject eye based on asize of a shape of the index captured at at least three positions withdifferent distances from the light-emitting surface to the subject'seye.
 7. An ophthalmologic apparatus comprising; an index projection unitconfigured to project an index on a cornea of a subject's eye; animaging unit configured to form an image on an imaging plane via anobjective lens and capture an image of the index projected on thecornea; and a control unit configured to control a distance between thesubject's eye and the object lens so that a size of the captured indexbecomes a predetermined size wherein the control unit obtains a workingdistance for the subject eye based on a size of a shape of the indexcaptured at a plurality of positions with different distances from thelight-emitting surface to the subject's eye.
 8. The ophthalmologicapparatus according to claim 7, further comprising: a driving unitconfigured to move a light-emitting surface of the index projection unitso as to change the size of the index, wherein a movement of the lightemitting surface by the driving unit is a reciprocation movement.
 9. Theophthalmologic apparatus according to claim 8, wherein the control unitcontrols the distance based on a relation between the size of thecaptured index and the distance from the light-emitting surface of theindex projection unit to the subject's eye.
 10. The ophthalmologicapparatus according to claim 7, further comprising: an illuminationoptical system configured to project a ring-shaped illumination light ona pupil of the subject eye; and an imaging optical system configured toform an image of a light flux of the illumination light reflected from afundus on the imaging plane via an object lens and capture a fundusimage.
 11. The ophthalmologic apparatus according to claim 10, whereinthe illumination optical system comprises a perforated mirror configuredto reflect illumination light, and wherein the index projection unit isdisposed in a hole portion of the perforated mirror.